Selectively coating bond pads

ABSTRACT

Solder ball bond pads and wire bond pads may be selectively coated so that the wire bond bond pads have a thicker gold coating than the solder ball bond pads. This may reduce the embrittlement of solder ball joints while providing a sufficient thickness of gold for the wire bonding process. In general, gold coatings are desirable on electrical contact surfaces to prevent oxidation. However, the thickness of gold which is necessary on solder ball bond pads may be less and excessive gold may be disadvantageous. Thus, by masking the solder ball bond pads during the gold coating of the wire bond bond pads, a differential gold thickness may be achieved which is more advantageous for each application.

BACKGROUND

[0001] This invention relates generally to coating bond pads in thefabrication of integrated circuits.

[0002] It is generally desirable to coat wire bond pads and solder ballbond pads with nickel and gold. Currently these coating processes areimplemented simultaneously on both types of bond pads. Wire bond bondpads typically need more gold than solder ball bond pads. Too littlegold causes wire bonding problems. Too much gold causes solder balljoint embrittlement.

[0003] As a result, in situations in which both types of bond pads arecontained on the same structure, conventional processing provides eithertoo much gold to suit the solder ball bond pads or too little gold tosuit the wire bond pads. Certainly, providing excessive gold coatings isgenerally not cost effective.

[0004] Thus, there is a need for a better way to coat bond pads infabricating structures with both solder ball and wire bond bond pads.

SUMMARY

[0005] In accordance with one aspect, a method of coating solder balland wire bond pads includes masking the solder ball pads. Gold is coatedon the wire bond pads with the solder ball pads masked.

[0006] Other aspects are set forth in the accompanying detaileddescription and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0007]FIG. 1 is a process flow for one embodiment of the presentinvention;

[0008]FIG. 2 is an enlarged cross-sectional view of a solder ball and awire bond pad after nickel plating;

[0009]FIG. 3 is an enlarged cross-sectional view of the embodiment shownin FIG. 2 after the solder ball bond pad has been masked;

[0010]FIG. 4 is an enlarged cross-sectional view corresponding to theembodiment shown in FIG. 3 after a thicker gold coat has been applied;

[0011]FIG. 5 is an enlarged cross-sectional view after the solder ballbond pads have been unmasked;

[0012]FIG. 6 is an enlarged cross-sectional view of the embodiment shownin FIG. 5 after a thinner gold coat has been applied;

[0013]FIG. 7 is an enlarged cross-sectional view of the finishedstructure in accordance with one embodiment of the present invention;

[0014]FIG. 8 is a process flow for another embodiment of the presentinvention;

[0015]FIG. 9 is an enlarged cross-sectional view of a solder ball and awire bond bond pad after the wire bond bond pads have been coated withgold;

[0016]FIG. 10 is an enlarged cross-sectional view after the solder ballbond pads have been unmasked;

[0017]FIG. 11 is an enlarged cross-sectional view after the wire bondbond pads have been masked;

[0018]FIG. 12 is an enlarged cross-sectional view after the solder ballbond pads have been coated; and

[0019]FIG. 13 is an enlarged cross-sectional view after the wire bondbond pads have been unmasked.

DETAILED DESCRIPTION

[0020] A process for differentially coating solder ball bond pads andwire bond pads, shown in FIG. 1, may begin, in one embodiment of thepresent invention, by nickel plating wire bond pads 26 and solder ballbond pads 24 as indicated in block 10 of FIG. 1. As used herein, theterm “coating” is intended to encompass conventional electrolytic andelectroless plating processes as well as aqueous immersion coatingprocesses. Thus, the term “coating” is intended to be broader thanconventional plating processes and is intended to refer to causing ametal layer to bond on top of another metal material.

[0021] Conventional techniques for nickel coating include immersionusing a chemical reducing agent such as sodium hypophosphate to reducenickel salts. Such coatings may result in alloys with four to twelvepercent phosphorus. However, conventional electrolytic and electrolessnickel plating processes may be utilized as well.

[0022] Referring to FIG. 2, a solder ball bond pad 24 may be positionedon a support structure 20 which also may bear a wire bond bond pad 26.In the illustrated embodiment, the solder ball bond pad 24 isillustrated as being larger than the wire bond bond pad. However, thepresent invention is not limited in any way to any particular geometryof the bond pads. The solder ball bond pad 24 has a nickel coating 28coated on it and the wire bond bond pad 26 is coated with a nickelcoating 30.

[0023] The solder ball bond pad 24 is then masked as indicated in block12 of FIG. 1. This is illustrated by the coating 32 in FIG. 3. Anysuitable masking material may be utilized as the coating 32 includingpatterned dry film resist.

[0024] Referring again to FIG. 1, a thicker gold coating is applied tothe wire bond bond pad 26, as indicated in block 14. No coating isapplied to the solder ball bond pad 24 which is masked off. Theresulting thicker gold coating 34, shown in FIG. 4, may be on the orderof 0.1 to about 0.4 microns in thickness.

[0025] Next the solder ball bond pad 24 may be unmasked, as indicated inblock 16. As illustrated in FIG. 5, the mask 32 has been removed, forexample using an etching technique. Thereafter, a thinner gold coatingmay be applied as indicated in block 18 in FIG. 1.

[0026] Thus, as shown in FIG. 6, a thinner gold coating 36 may beapplied over the nickel coating 28 on the solder ball bond pad 24. Thesame coating may be added to the coating 34 applied to the wire bondbond pad 26 to form a composite gold layer 38. Any of a variety ofcoating techniques, including electroless coating, immersion, andelectrolytic plating, may be utilized to form the thinner gold coating.

[0027] While the coating is applied in two steps to the wire bond bondpads in the embodiments illustrated in FIGS. 1-6, it is also possible toprovide the wire bond gold coating in one single step and then to maskoff the wire bond bond pads to provide the thinner gold coating only onthe solder ball bond pads.

[0028] As a result of the processing described above, the solder ballbond pads may have a gold coating with a thickness on the order of 0.1to about 0.3 microns. One advantageous coating thickness is about 0.25microns. In general, it is desirable to provide a coating thickness onthe solder ball bond pads which is sufficiently small to reduce solderball joint embrittlement. It is also desirable to have a coating whichis thick enough to prevent oxidation.

[0029] At the same time, it is desirable to provide a conventionalthickness of gold on the wire bond bond pads to provide a good wire bondwhen using conventional wire bond bonding techniques. A suitable goldcoating 38 thickness on the wire bond bond pads is about 0.5 microns.

[0030] In some embodiments of the present invention, the solder ballbond pad 24 may be copper or copper coated. The wire bond bond pad 26may be formed, for example, of aluminum. However, other materials whichare compatible with gold coating techniques may also be used.

[0031] Referring to FIG. 7, one embodiment of a package 52 made inaccordance with the techniques described above includes a laminate core20. The laminate core 20 may be formed of an insulating material havinga plurality of internal trace layers (not shown). Interconnections maybe formed between various trace layers and the bond pads 40 and 42contained on a surface of the core 20. The bond pads 40 may be solderball bond pads for coupling to solder balls (not shown). The bond pads42 may be wire bond bond pads for coupling to bonding wires 50 also wirebonded to a die 44 through an opening 46 in the laminate core 20.

[0032] The solder ball bond pads 40 and wire bond bond pads 42 on thesame surface may be gold coated to different thicknesses, as describedabove, to achieve a more desirable performance.

[0033] As illustrated in FIG. 8, in accordance with another embodimentof the present invention, the solder ball and wire bond bond pads arenickel coated as indicated in block 60. This step is illustrated in FIG.2. Next, the solder ball bond pads are masked as indicated in block 62and FIG. 3.

[0034] The wire bond bond pads 26 are coated as indicated in block 64.In this embodiment, the wire bond bond pads 26 are coated in one step tothe full desired thickness. The wire bond bond pad coating is indicatedat 76 in FIG. 9. The masking layer over the solder ball bond pads isindicated at 32.

[0035] Next the solder ball bond pads are unmasked as indicated at block66 in FIG. 8. As shown in FIG. 10, the mask 32 has been removed forexample by etching.

[0036] Referring again to FIG. 8, the wire bond bond pads are masked asindicated in block 68. The mask 78 is shown in position over the wirebond bond pads 26 in FIG. 11.

[0037] The solder ball bond pads 24 may then be coated as suggested inblock 70 and as illustrated at 80 in FIG. 12. The wire bond bond pads 26may be unmasked (block 72 in FIG. 8). As shown in FIG. 13, the mask 78has been removed. In some embodiments, different coating techniques maybe used for solder ball versus wire bond bond pads.

[0038] While the present invention has been described with respect to alimited number of embodiments, those skilled in the art will appreciatenumerous modifications and variations therefrom. It is intended that theappended claims cover all such modifications and variations as fallwithin the true spirit and scope of this present invention.

What is claimed is:
 1. A method of coating solder ball and wire bondbond pads comprising: masking said solder ball bond pads; and coatinggold on said wire bond bond pads with said solder ball bond pads masked.2. The method of claim 1 including providing a different gold coatingthickness on said solder ball bond pads and said wire bond bond pads. 3.The method of claim 2 including providing a thicker gold coating on saidwire bond bond pads than on said solder ball bond pads.
 4. The method ofclaim 3 including providing a gold coating, on said wire bond bond pads,having a thickness of about 0.5 microns and providing a solder ball bondpad gold coating of approximately 0.1 to 0.3 microns in thickness. 5.The method of claim 1 including nickel coating said solder ball and saidwire bond bond pads at the same time before coating said wire bond bondpads with gold.
 6. The method of claim 1 including coating said wirebond bond pads with a first gold coating and coating both of said solderball bond pads and said wire bond bond pads with a second gold coating.7. The method of claim 6 wherein said second gold coating is thinnerthan said first gold coating.
 8. The method of claim 1 including usingan electroless plating technique to coat gold on said wire bond bondpads.
 9. The method of claim 1 including forming a laminate structurehaving solder ball bond pads and wire bond bond pads on the samesurface.
 10. The method of claim 1 wherein said solder ball bond padsare gold coated in a single step.
 11. The method of claim 10 includingcoating said solder ball bond pads and said wire bond bond pads whilethe other of said solder ball and wire bond bond pads is masked.
 12. Amethod of coating two different types of bond pads on the same surfacecomprising: masking off a first type of bond pad; and coating a metal onthe second type of bond pad with said first type of bond pad beingmasked.
 13. The method of claim 12 including masking solder ball bondpads.
 14. The method of claim 13 including coating metal on wire bondbond pads.
 15. The method of claim 14 including coating gold on saidwire bond bond pads.
 16. The method of claim 15 including unmasking saidsolder ball bond pads and coating a metal on both said wire bond bondpads and said solder ball bond pads.
 17. The method of claim 12including providing different coating thicknesses on said first andsecond types of bond pads.
 18. The method of claim 12 including coatinggold on said second type of bond pad.
 19. The method of claim 18 whereinsaid first type of bond pad is a solder ball bond pad and said secondtype of bond pad is a wire bond bond pad, coating gold on said wire bondbond pad to a thickness of about 0.5 microns and coating gold on saidsolder ball bond pads to a thickness of about 0.1 to about 0.3 microns.20. The method of claim 19 including nickel coating said first andsecond types of bond pads at the same time before coating said wire bondbond pads with said metal.
 21. The method of claim 12 including coatingboth said first and second types of bond pads with said metal aftercoating said metal on said second type of bond pad.
 22. The method ofclaim 12 including masking off said second type of bond pad and coatingmetal on said first type of bond pad.
 23. A method of forming solderball and wire bond bond pads comprising: forming a solder ball bond pad;coating gold over said solder ball bond pad; forming a wire bond bondpad; and coating gold over said wire bond bond pad to a thicknessgreater than said gold coating over said solder ball bond pad.
 24. Themethod of claim 23 including masking said solder ball bond pad andcoating gold on said wire bond bond pad with said solder ball bond padmasked.
 25. The method of claim 24 including providing a gold coating onsaid wire bond bond pad having a thickness of about 0.5 microns.
 26. Themethod of claim 23 including providing a gold coating on said solderball bond pad of approximately 0.1 to 0.3 microns in thickness.
 27. Themethod of claim 23 including coating said wire bond bond pads with afirst gold coating and coating both of said solder ball and said wirebond bond pads with a second gold coating.
 28. The method of claim 23including coating said solder ball bond pad to a thickness ofapproximately 0.25 microns.
 29. A method of forming solder ball and wirebond bond pads comprising: masking said solder ball bond pad; coatinggold over said wire bond bond pad; masking said wire bond bond pad; andcoating gold over said solder ball bond pad.
 30. The method of claim 29including coating said wire bond bond pad with gold to a thicknessgreater than the gold coating over said solder ball bond pad.
 31. Apackaged integrated circuit device comprising: a plurality of goldcoated solder ball bond pads; a plurality of gold coated wire bond bondpads; and the gold coating on said solder ball bond pads being thinnerthan the gold coating on said wire bond bond pads.
 32. The device ofclaim 31 wherein the thickness of the gold on said solder ball bond padsis sufficiently low to reduce the likelihood of solder ball jointembrittlement.
 33. The device of claim 31 wherein said solder ball bondpads have a gold coating having a thickness of between about 0.1 and 0.3microns.
 34. The device of claim 33 wherein said solder ball bond padgold coating has a thickness of about 0.25 microns.
 35. The device ofclaim 33 wherein said wire bond bond pads have a gold coating thicknessof approximately 0.5 microns.
 36. The device of claim 31 wherein saidsolder ball bond pads and said wire bond bond pads are all contained onthe same planar surface.